1. Technical Field
The present disclosure relates to an engine rotational speed display device, and particularly to an engine rotational speed display device of a vehicle equipped with a continuously variable transmission having manual transmission mode in which the transmission is shifted according to a gear shift operation of a driver.
2. Related Art
The characteristics such as the output (horsepower, torque) and fuel consumption amount of an engine significantly vary with the rotational speed of the engine. Thus, a conventional vehicle is generally equipped with a display device (tachometer) for informing a driver of the engine rotational speed. Such an engine rotational speed display device has various known types including mechanical type, electrical type, and digital type. For example, an engine rotational speed is calculated from time variation in rotational position of a crankshaft, the rotational position being obtained from output signals of a crank angle sensor, and for example, an electric motor is driven according to a result of the calculation so as to actuate a meter (needle).
For example, Japanese Unexamined Patent Application Publication No. H01-154195 discloses such an engine rotational speed display device, in which a counter setting value is defined to be large (determination period is set to be long) at the time of low rotation that is close to the idling engine speed, and the counter setting value is defined to be small (determination period is set to be short) at the time of middle to high rotation. The determination period is controlled to be reduced according to an increase in engine rotational speed, thereby implementing the technology that prevents a variation in rotational speed display due to varying engine rotational speed at the time of low rotation and ensures responsiveness for quick change in engine rotational speed at the time of high rotation.
In recent years, some vehicles have become commercially practical, in which the output characteristic of the engine and the transmission characteristics and the transmission mode of a continuously variable transmission (or an automatic transmission) are selectable (switchable) according to the preference of a driver. More specifically, the vehicles have become commercially practical, in which the output characteristic of the engine may be freely selected by choosing, for example, one of three modes, that is, normal mode, save mode, and power mode, the normal mode being suitable for normal driving, the save mode achieving low fuel consumption by reducing the output torque, the power mode being focused on power drive and achieving output characteristics having an excellent response in a rotational speed range including a low rotational speed range and a high rotational speed range. In addition, the transmission mode of the continuously variable transmission is selectively switchable between automatic transmission mode and manual transmission mode, the automatic transmission mode allowing a transmission ratio to be changed automatically according to a running state of the vehicle, the manual transmission mode allowing a transmission ratio to be changed according to a gear shift operation (manual operation) of a driver.
For example, when manual transmission mode is selected and a gear shift operation of a driver is received in such a vehicle, a response delay normally occurs before the gear shift operation of the transmission is actually started and the engine rotational speed changes accordingly. For this reason, if detected engine rotational speed is displayed as it is, the needle indicating the engine rotational speed starts to move with a slight delay after the gear shift operation of the driver.
On the other hand, for example when power mode, which allows more sporty running, is selected as the engine output characteristic, movement of the needle indicating the engine rotational speed is demanded to have a good response and give sporty impression to the driver. However, it is expected that increased deviation between the movement (change) of the needle indicating the engine rotational speed and the actual movement (change) of the engine rotational speed may give sense of incongruity to the driver.